Broadband (spread-spectrum) radio frequency (RF) signals may be susceptible to narrowband interference signals that may increase the error rate when decoding transmitted data or potentially jam the broadband signal. In this regard, strong continuous-wave (CW) or slowly-modulated signals having a frequency band smaller than the broadband signal may have sufficient power spectral density (PSD) to disrupt the reception and decoding of the broadband RF signal. As an illustrative example, long-distance ultra-low-frequency (ULF) communication may be susceptible to ground station antennas generating intentional or unintentional narrowband signals that may interfere with broadband ULF signals. Further, characteristics such as the frequency bands, the signal strength, or the number of narrowband interference signals are often unknown to the receiver of the broadband signal, which may present challenges for designing systems to mitigate the impact of the narrowband signals.